To realize appropriate fuel-injection timing and appropriate ignition timing suited for a specified cylinder, a multi-cylinder internal combustion engine requires cylinder-identification for an engine cylinder to be brought into the next combustion stroke. Almost all of four-stroke cycle internal combustion engines employ a cam angle sensor configured to be synchronized with rotation of a camshaft that rotates in synchronism with rotation of a crankshaft such that one revolution of the camshaft is achieved at 720° crankangle, in addition to a crankangle sensor for detecting a rotational position of the crankshaft. In order to identify engine cylinders and also to identify the current position in phase in terms of crankangle during an operating cycle of each of the cylinders, such a four-stroke cycle internal combustion engine generally uses a pulse signal (unit pulses) generated from the crankangle sensor at each unit crankangle, often called “a POS signal”, as well as a pulse signal generated from the cam angle sensor at each interval between cylinders (i.e., at each phase difference between cylinders, for example, at each 180° crankangle in the case of a four-cylinder engine), often called “a PHASE signal”, the generated PHASE signals differing from each other.
In contrast to the above, Patent document 1 discloses a technique in which in a four-stroke cycle internal combustion engine employing an odd number of cylinders, a position in phase of each of the cylinders can be detected without depending on a cam angle sensor. This technique teaches the use of an intake manifold pressure signal (or an engine revolution speed signal), fluctuating in conjunction with each of operating cycles, in addition to the use of a unit pulse signal generated from a crankangle sensor having a pulse-defect portion, (i.e., a gap portion or a toothless portion) at each unit crankangle, thereby detecting a reversal between an increase and a decrease in the intake manifold pressure signal near the gap portion, generated at each 360° crankangle, or deriving an extreme (a local maximum or a local minimum) of a change in the intake manifold pressure near the gap portion. In this manner, the current stroke of the operating cycle of each of the cylinders is determined.
In the technique disclosed in the previously-discussed Patent document 1, a gradient of the intake manifold signal (or a gradient of the engine revolution speed signal) can be calculated by differentiating its signal value with respect to time, so as to detect a reversal between an increase and a decrease in the intake manifold pressure signal near the gap portion or calculate an extreme (a local maximum or a local minimum) of a change in the intake manifold pressure near the gap portion. However, the previously-discussed technique has the following drawbacks. Due to an unavoidable disorder of the intake manifold pressure signal, there is a possibility that a plurality of extremes (that is, a plurality of increase/decrease reversals) are detected. Due to a slight phase shift of the intake manifold pressure signal, there is a possibility that a gradient of the signal in a narrow range of pulse-defect portion (or in a narrow range of gap portion) is reversed. This leads to a deterioration in detection reliability, and hence it is impossible to more certainly achieve high-precision cylinder-identification.
Additionally, owing to the use of the derivative, which is the rate of change of the input signal with respect to time, even when the intake manifold pressure signal is used as the input signal, the derivative may be unavoidably affected by a change in engine revolution speed. For instance, in a transient operating situation, such as during cranking and starting period, due to a rapid engine-speed rise or undesirable engine-speed fluctuations, the detection accuracy may be further lowered.